A longstanding problem in recoilless weapon systems, such as recoilless rifles, projectile launchers and the like, has been the large amounts of unburnt propellant that exits from recoilless weapon systems. Propellant loss can account for as much as 30% of the total propellant charge weight. In large caliber systems, this problem can be even more pronounced due to the large amount of propellant needed to operate the system as well as the large exit nozzle area needed to maintain recoillessness.
Heretofore, several different cartridge case and propellant chamber configurations have been employed for recoilless weapon systems including large caliber weapons that require holding large amounts of propellant charge and for igniting the charge. Various perforated cartridge case designs are known and have been used. For example, a perforated cartridge case where propellant ignited inside the perforated case has been used in conjunction with a kidney-shaped exit nozzle where the gases expand radially outwardly into the propellant chamber and then exit through the nozzle. Such nozzle design is limited in efficiency in terms of recoillessness and perforated cartridge cases have been used in conjunction with a blowout disc for more efficient central nozzle designs. A blowout disc is employed in such systems to control the amount of combustion which takes place prior to gas discharge by confining the propellant gas until the disc ruptures, the disc having a great influence on the amount of unburnt propellent loss during the initial stage of burning. In such design, the propellant gases generated pass through the cartridge case perforations into the annular chamber and then, after rupture of the blowout disc, the gases pass from the chamber back across the cartridge case wall and out through the nozzle. However, while the blowout disc has a great deal of influence on the loss of propellent during the initial stage of burning, the blowout disc in itself is a projectile which exits from the weapon through the nozzle. Further, the bigger the weapon, the more rigid the disc must be to contain the pressure in the chamber to facilitate proper propellant burning. Other known designs include frangible cartridge cases wherein the case is destroyed during firing of the weapon, and the use of the principle of exposed strip propellant mounted along the inner chamber wall. However, the frangible case design can adversely influence the interior ballistics of the weapon by the manner in which burning of the case can affect the propellant ignition and combustion, and the exposed propellant strip design has a disadvantage in effecting proper ignition of the propellant, large chunks of propellant generally breaking off and blowing out of the central nozzle during ignition and burning of the propellants.
When using a central orifice nozzle design, the case designs heretofore employed generally require the use of a blowout disc in the throat of the nozzle which, as indicated, in large caliber weapons must be quite rigid to contain the pressures in the chamber and facilitate proper propellant burning, increasing the danger of the disc as projectile when exiting the weapon. Moreover, conventional designs require the entire chamber to be pressurized to insure proper propellant ignition and employ the principle of radially expanding gases in a large volume chamber. The large amounts of propellants required to supply enough gas to pressurize the system generally results in large amount of unburnt propellant being thrown about the chamber and then blown out and lost through the nozzle.